The treatment of paper-making fibers to render paper made therefrom stronger has a long history of development. Many different chemical additives have been utilized for this purpose. Cationic starches are exemplary, but suffer from being inconsistent in performance, incompatible with other additives, etc. Amino-aldehyde resins have been used to impart wet strength to paper both as resins per se and as acid colloids thereof, see U.S. Pat. No. 2,345,543; U.S. Pat. No. 2,485,079; U.S. Pat. No. 2,485,080; U.S. Pat. No. 2,559,220; U.S. Pat. No. 2,986,489.
In U.S. Pat. No. 3,594,271, there is disclosed the reaction product of a water-soluble starch and a melamine-formaldehyde acid colloid as a dry strength imparting additive for paper. This patent teaches the use of a partially or fully polymerized (condensed) melamine-for-maldehyde resin in the formation of the acid colloid and the reaction of the acid colloid with the starch. While relatively effective, it never proved to be a commercial success because it was not as cost effective as existing products.
U.S. Pat. No. 4,461,858 discloses the manufacture and use of a polyvinyl alcohol/melamine-formaldehyde resin acid colloid in the treatment of paper. The reaction product is said to impart increased processing capability and improved wet and dry strength to the paper. The increased processing capabilities are said to constitute easier process control, and better retention of fines. While the polyvinyl alcohol/melamine-formaldehyde resin acid colloid products have achieved moderate commercial success, they still leave something to be desired in that they are very difficult to prepare in that the process is cumbersome and time consuming, they do not possess a very long storage life they are relatively expensive and they normally must be prepared at the site of the paper mill and at low solids.